<p>The implicit achievement motive (<i>n</i>Achievement) typically shows positive effects on individuals’ performance in different achievement contexts. Recent findings suggest that this association is furthermore qualified by other personality dispositions. Still, research on achievement-related moderators of the effect of <i>n</i>Achievement on objective performance remains sparse, specifically in children and adolescents. In the present study, we examined the relationship of <i>n</i>Achievement on swimming performance by considering effects of competitive anxiety. We hypothesized a positive link between <i>n</i>Achievement and swimming performance, but only when competitive anxiety is weakly or moderately pronounced. We assessed data of 139 German children and adolescents (75 girls) aged between 7 and 18 years. Results mostly support our hypotheses. There was no significant main effect of <i>n</i>Achievement on swimming performance. However, competitive anxiety interacted significantly with <i>n</i>Achievement in predicting sports performance: <i>n</i>Achievement showed a positive association with objective swimming performance only in participants with weakly pronounced competitive anxiety. Findings are discussed with respect to existing models of <i>n</i>Achievement and competitive anxiety as well as their conjoint significance for performance in sports contexts.</p>